Description

While combustion-based heating systems have been in widespread use in cold regions, air source heat pumps have been gathering attention as alternative heating devices owing to the high levels of energy efficiency they provide. However, conventional air source heat pumps had previously required intermittent operation to melt the frost forming on the outdoor unit of the heating system during heating within environments characterized by lower outdoor air temperatures. The resultant room temperature drops would end up making residents uncomfortable.

To solve this problem, there has been proposed in the past a refrigerant circuit serving to perform continuous heating. This circuit involves the installation of hot gas bypass valves within the outdoor unit. The outdoor heat exchanger is then divided into two parts in parallel, with one being used for heating and the other supplied with high-temperature gas refrigerant that is discharged from the compressor for defrosting. However, an issue arose: sensible heat resulting from the use of a gas refrigerant presented low amounts of heat, which meant that defrosting would require a high flow rate of the refrigerant. This would result in a shortage of refrigerant to be used for indoor heating and a drop in terms of the warm discharge-air temperature indoors.

An effective means to improve heating capacity is to reduce the flow rate of the refrigerant used for defrosting as much as possible and to ensure a high flow rate in terms of the refrigerant used for indoor heating. Therefore, a focus was placed on utilizing the latent heat generated by the condensation of the refrigerant for defrosting to develop a new refrigerant circuit and a new technology which serves to control refrigerant pressure. Specifically, two pressure-regulating valves have been installed at the upstream and downstream portions of the heat exchanger to be subject to defrosting. The refrigerant circuit has been configured in a manner which has the refrigerant used for defrosting returning to the mainstream via the upstream portion of the heat exchanger (which works as an evaporator). Furthermore, the refrigerant pressure was controlled in order to have the gas refrigerant become condensed at a temperature above the melting point of the frost. As a result, the flow rate of the refrigerant required for defrosting was reduced to 1/6 of that seen with the conventional method (which involves the utilization of the sensible heat of the refrigerant). Heating capacity during defrosting was improved by 30% when the outdoor air temperature was 36 °F (2 °C) as the result of an increase in the flow rate of the refrigerant supplied to the indoor units. Additionally, it was confirmed that continuous heating was possible even when temperatures were below freezing, which was not possible when utilizing the conventional method.

Citation: 2021 Virtual Conference Papers

Product Details

Published:

2021

Number of Pages:

9

Units of Measure:

Dual

File Size:

1 file , 1.2 MB

Product Code(s):

D-VC-21-C057